schieren



March 31, 19.64 K. H. SCHIEREN 3,127,015

HOT DEF'ORMATION OF METALS Filed April 29. 1960 2 Sheets-Sheet 1 In 2Karl HEM/ lP/HV Attorneys March 31, 1964 H. SCHIEREN 3,127,015

HOT DEFORMATION OF METALS Filed April 29. 1960 2 Sheets-Sheet 2Attorney: 1

United States Patent 3,127,015 HOT DEFORMATEON 0F METALS Karl HeinzSchieren, Duisburg, Germany assrgnor to The Loewy Engineering CompanyLimited Filed Apr. 29, 1960, Ser. No. 25,711 Claims. (Cl. 207-) Thisinvention relates to the hot deformation of metals by extrusion (with orwithout the use of a mandrel), piercing or die-forging.

The primary object is to prolong the life of the tools, namely the dies,mandrels and punches used in such processes by improving theirlubrication and in so doing also to reduce the pressure required todeform a given metal.

According to the invention a material interposed between the metal andthe surface of a die, mandrehor punch for the purpose of lubricating thesurface consists wholly or substantially wholly of normally solidorganic material which burns or volatilises when trapped bet-ween thehot metal and the surface and subjected to the operating pressure.

The organic material is preferably polyethylene or polyvinyl chloridebut it may be any other material which will be converted completely orsubstantially completely into gas under the stated conditions. Broadlyspeaking all synthetic polymers will be so converted.

A lubricant that is in use at the present time consists of a mixture ofsubstances including graphite, carbonaceous materials and a source ofoxygen, the graphite being the predominating constituent. This lubricantpartially vapourises under the working temperature and pressure. Thelubrication in this case is mainly effected by the graphite, but thegases evolved are said to contribute to the lubrication.

It is of the essence of the present invention that no graphite or otherlamellar lubricant is used to lubricate the die or mandrel and I believethat in fact all or substantially all the lubrication of the tool iseffected by a film of gas produced from the organic material at theoperating pressure and temperature. However this may be, the result isincreased tool life in comparison with that obtained when thegraphite-containing lubricant referred to above is used.

The organic material may be used as a moulding, which can easily bepreformed to fit a given die and can very easily be put in position.However the organic material preferably is in the form of a powder orgranules, bound to or enclosed in a combustible carrier, since then theexpense of converting the material into a moulding is avoided.

The invention can be applied with advantage to the extrusion of tubingwith the use of a mandrel that passes through the die. In this case themandrel may be covered or coated with the organic solid material andlubricated by the gases evolved from it. However the mandrel may belubricated only by gases evolved from organic solid material interposedbetween the hot metal and the die, that is to say, the mandrel need notitself be covered or coated with the organic material, though when it isso covered or coated the inner surface of the extruded tubing is ofbetter quality than that obtained by normal methods of lubrication.

This invention will be more clearly understood by ref erence to theaccompanying drawings, in which:

FIGURE 1 diagrammatically shows part of one extrusion press just beforeextrusion begins;

FIGURE 2 is a section through one carrier of powdered organic material;

FIGURE 3 is a plan of this carrier; and

FIGURES 4 and 5 illustrate a die-forging operation.

Fee

The press shown in FIGURE 1 is of the kind in which there is a container1 and a movable die-carrier 2 which brings dies successively intoregister with the outlet of the container, one die being shown at 3. Thepress is intended for the production of tubing from steel, and itincludes an annular pressing stem 4 with a pressing disc 4a and amandrel 5 which after entering the container move as a unit during theextrusion operation.

The press is shown at the moment when an annular billet 6 is in thecontainer and the pressure is about to be applied.

The die .3 has a frusto-conical mouth, and before it is brought intoregister with the end of the container 1 a moulding 7 of polyethylenewhich mates with the frustoconical face of the die and has a hollowspigot that extends into the die opening proper is inserted in it. Thereason for using a moulding with a cylindrical spigot is that the diecarrier '2 turns at high speed to bring the die 3 into position, and itis necessary that the moulding 7 should be held in the die during thismovement by the frictional engagement of the spigot in the die.

FIGURE 1. also shows a paper sleeve 8, to which powdered organicmaterial is bound, in position on the mandrel 5. This sleeve is pushedover the mandrel before the introduction of the mandrel into thecontainer. The powdered organic material may be bound to the paper by amixture of triohloroethy-lene and polystyrol or by cold glue.

When the hot billet 6 is initially brought into contact with themoulding 7 a little smoke is evolved but there is substantially nodevelopment of gas until the billet is subjected to the extrusionpressure. Immediately after the pressure is applied tlere is intensedevelopement of gas, and provided that the polyethylene or polyvinylchloride is present in adequate amount the gas serves to lubricate thesurface during the whole of the extrusion process. The polyethylene orpolyvinyl chloride is not wholly converted into gas, and surprisingly asmall tarry residue of the combustion is found to adhere to the leadingend of the extruded tubing.

As an example, in the extrusion of a hollow billet of stainless steel totubing over an uncovered mandrel through a die with an entrance angle of27, the die being made of 9% tungsten steel, I have found that amoulding 7 of polyvinyl chloride 2 mm. thick serves to lubricatecompletely a billet 380 mm. long, 164 mm. in outside diameter to producetube of 62 mm. outside diameter and 50' mm. inside diameter, theextrusion ratio being 18:1 and the length of the tube being over 6meters. In this example the inner wall of the extrusion container waslubricated with a mixture of oil and graphite in the usual way.

A particularly convenient way of using an organic material in the formof powder or granules is to mix these with a binder and enclose themixture between two pieces of paper. A unit so formed is shown at 9 inFIGURES 2 and 3 and consists of two pieces 10 of corrugated paper of thedesired size and shape, with the mixture of the organic material andbinder 11 enclosed between them as in a sandwich. For use in a unit ofmm. external diameter and 65 mm. internal diameter the mixture mayconsist, for example, of 60 grams of polyethylene, 35 grams ofpolystyrol and litre of trichlorethylene, and it hardens when putbetween the pieces of paper.

If the unit 9 is to be used with a die held in a rotary carrier, it isput into position when the die is out of register with the container andmust be frictionmly held in position. For this purpose a spigot 12 isprovided and consists of a tube 13 with a flange 14 which is pushed intothe mixture 11 before this hardens. The tube 13- may be of sheet metal,cardboard or any other convenient material.

The unit 9 can be handled with ease, and the corrugated paper acts asthermal insulation to prevent premature combustion or volatilisation ofthe organic material when the unit comes into contact with a hotsurface.

A sleeve to be put over a mandrel may also be made as a sandwich.

In the die-forging process illustrated by FIGURES 4 and 5 flat discs areused and overlap the effective area of dies 16 as shown in FIGURE 5. Onedisc 15 is put in the bottom die, the hot metal 17 is then put on it andanother disc 15 is put on top of the hot metal immediately before theupper die is brought down.

I find that in an extrusion process the air available in the containerof the press is adequate for the production of the gases by chemicalreaction with the polyvinyl chloride or other material, but if necessaryadditional oxygen may be supplied. For example the moulding 7 may becovered with a layer of an oxidising agent or a material containingexcess oxygen may be incorporated in the mixture 1 1. An example of asuitable oxidising agent in manganese dioxide. The oxidising agent willnot be completely converted into gas and accordingly its presence isundesirable. If such an oxidising agent is used, therefore, it should bepresent in only a small amount, say not more than 5% by weight of theorganic solid material.

The great advantage obtained by means of the invention is shown by testsmade with one extrusion press used for the production of tubing ofstainless steel containing about 18% chromium and 9% nickel With a smallamount of titanium, the die being normally lubricated by a mixture ofgraphite and combustible materials. The average life of the dies in thisparticular press is 35 extrusions. The quality of the surface of theextruded stainless steel is such that from 50 to 70% of the tubes mustbe ground to remove surface blemishes. The average pressure requiredduring the extrusion is about 84,000 p.s.i. measured on thecross-section of the billet.

On replacing the graphite lubricant by polyvinyl chloride in the form ofmouldings 2 mm. thick, but making no other change, the average die lifewent up to 54 extrusions, the average number of tubes that neededgrinding fell to below 50% and the average extrusion pressure fell toabout 78,500 p.s.i.

When a more heat-resistant steel, containing about 18% chromium, 11.5%nickel and 2.2% molybdenum, was extruded with an extrusion ratio of 18:1the average life of the dies with the graphite lubricant was 1 1extrusions and the average pressure during the extrusion was about97,500 p.s.i. On replacing the lubricant by mouldings of polyvinylchloride 2 mm. thick the average life rose to 24 extrusions and theaver-age pressure fell to about 89,700 psi.

The work normally carried out on a 1700 ton press requires only a 1530ton press. Or conversely a 1700 ton press in which a lubricant accordingto the invention is used can extrude at a higher extrusion ratio thanwas heretofore possible, so that the output which can be obtained fromthe press is increased. These advantages are additional to the increasein tool life.

I claim:

1. In a method of producing a shaped metal body by subjecting a metalwork-piece heated to a plastic, condition to a metal shaping operationusing shaping dies and pressure, the steps which comprise interposingbetween said heated Work-piece and said shaping dies a lubricant layerconsisting of a wholly solid organic material which becomes gaseous"when under operating pressures between the hot metal work-piece and theshaping dies and applying pressure and vaporizing the wholly solidorganic material whereby the vapor acts as the lubricant.

2. The method of claim 1 wherein the said organic material is a solidpolymer selected from the group consisting of polyethylene and polyvinylchloride.

3. The method of claim 1 wherein the organic material is in the form ofa moulding.

4. The method of claim 1 wherein the organic material is retained in acombustible carrier.

5. The method of claim 1 wherein the organic material is a hardenedmixture of polyethylene and polystyrol between sheets of corrugatedpaper.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Paper Number 57-LUB-1, Oct. 7-9, 1957, pub. by ASME, 29 W.39th St., New York 18, N.Y., pp. 1-13. The Extrusion of Metals, byClaude E. Pearson, 1953,

0 John Wiley and Sons, Inc., 440 4th Ave., New York, p.

1. IN A METHOD OF PRODUCING A SHAPED METAL BODY BY SUBJECTING A METALWORK-PIECE HEATED TO A PLASTIC CONDITION TO A METAL SHAPING OPERATIONUSING SHAPING DIES AND PRESSURE, THE STEPS WHICH COMPRISE INTERPOSINGBETWEEN SAID HEATED WORK-PIECE AND SAID SHAPING DIES A LUBRICANT LAYERCONSISTING OF A WHOLLY SOLID ORGANIC MATERIAL WHICH BECOMES GASEOUS WHENUNDER OPERATING PRESSURES BETWEEN THE HOT METAL WORK-PIECE AND THESHAPING DIES AND APPLYTERIAL WHEREBY THE VAPOR ACTS AS THE LUBRICANT.